使用多个音频类型的 AVAssetTrack 切换 AVURLAsset 的音频轨迹

Question

我有一个 AVURLAsset 和多个音频类型的 AVAssetTrack。我希望能够允许用户通过触摸按钮在这些不同的音轨之间切换。它可以打开和关闭第一首曲目的音量，但当音量设置为 1.0 时听不到其他曲目。

以下是用于调整轨道音量的代码（发送者是一个 UIButton，其标签设置为 audioTracks 中资产的索引）。

AVURLAsset *asset = (AVURLAsset*)[[player currentItem] asset];
NSArray *audioTracks = [asset tracksWithMediaType:AVMediaTypeAudio];


NSMutableArray *allAudioParams = [NSMutableArray array];
int i = 0;
NSLog(@"%@", audioTracks);
for (AVAssetTrack *track in audioTracks) {
    AVMutableAudioMixInputParameters *audioInputParams =    [AVMutableAudioMixInputParameters audioMixInputParameters];
    float volume = i == sender.tag ? 1.0 : 0.0;
    [audioInputParams setVolume:volume atTime:kCMTimeZero];
    [audioInputParams setTrackID:[track trackID]];
    [allAudioParams addObject:audioInputParams];
    i++;
}
AVMutableAudioMix *audioZeroMix = [AVMutableAudioMix audioMix];
[audioZeroMix setInputParameters:allAudioParams];

[[player currentItem] setAudioMix:audioZeroMix];

我需要做些什么才能使所需的曲目成为活动曲目吗？

Answer 1

好的，发现问题了。与上面的代码无关，因为这工作正常。问题是除第一个轨道之外的音频 AVAssetTracks 未启用。要启用它们，必须使用 AVMutableComposition 重新创建资产：

NSURL *fileURL = [[NSBundle mainBundle]
                  URLForResource:@"movie" withExtension:@"mp4"];

AVURLAsset *asset = [AVURLAsset URLAssetWithURL:fileURL options:nil];

AVMutableComposition *composition = [AVMutableComposition composition];

AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
NSError* error = NULL;

[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,asset.duration) 
                               ofTrack:[[asset tracksWithMediaType:AVMediaTypeVideo]objectAtIndex:0] 
                                atTime:kCMTimeZero
                                 error:&error];

NSArray *allAudio = [asset tracksWithMediaType:AVMediaTypeAudio];
for (int i=0; i < [allAudio count]; i++) {
    NSError* error = NULL;
    AVAssetTrack *audioAsset = (AVAssetTrack*)[allAudio objectAtIndex:i];

    AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    [compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero,asset.duration) 
                                   ofTrack:audioAsset
                                    atTime:kCMTimeZero
                                     error:&error];

    NSLog(@"Error : %@", error);

}